According to energy and momentum conservation, two discriminating variables, the energy difference \(\Delta E\)  and beam-constrained mass \(M_{\textrm {BC}}\) , are utilized to identify the \(\Lambda _{c}\)  signals. The energy difference is defined as \(\Delta E~\equiv ~E~-~E_{\textrm {beam}}\) , where \(E\)  is the energy of the \(\Lambda _{c}\)  candidate and \(E_{\textrm {beam}}\)  the mean energy of the two colliding beams. In each tagged mode, the \(\Lambda _{c}\)  candidates are formed by all possible combinations of the final state particles, and only the one with minimum \(|\Delta E|\)  is stored. In the following analysis, events are rejected if they fail the \(\Delta E\)  requirements specified in Ref. [1]}. The beam-constrained mass is defined as \(M_{\textrm {BC}}c^{2}\equiv \sqrt{E_{\textrm {beam}}^{2}-p^{2}c^{2}}\) , where \(p\)  is the momentum of the \(\Lambda _{c}\)  candidate. Both \(\Delta E\)  and \(M_{\textrm {BC}}\)  are calculated in the initial \(e^{+}e^{-}\)  CM system. In Fig. REF , the \(M_{\textrm {BC}}\)  distributions for \(\Lambda _{c}^{+}\rightarrow pK^{-}\pi ^{+}\)  at the four CM energies are shown. Clear peaks at the nominal \(\Lambda _{c}^{+}\)  mass are observed. Studies of the inclusive MC samples show that the cross feeds among the ten tagged modes are less than 1.5% and the background shape can be described by the ARGUS function [2]}.
